Syriske regjeringsstyrker støttet av Hizbollah har gjenerobret deler av byen Qusayr i Homs-provinsen på grensen til Libanon.

The small city, about 100 miles northwest of the Syrian capital, Damascus, is crucial to supply routes for both sides. Qusayr is a conduit for rebel supplies and fighters from Lebanon, and it links Damascus to the Mediterranean coast, which is the heartland for Mr. Assad’s minority Alawite sect.

The Syrian government appears to be trying to regain as much territory as possible to strengthen its negotiating position while Russia and the United States try to organize peace talks for next month.

The rebels have issued pleas for help, saying they are running out of ammunition. A Syrian opposition figure with ties to the Saudi government, who spoke on condition of anonymity, said on Sunday that support and ammunition from Persian Gulf countries is reaching insurgents in Qusayr, but added that the government’s increasing control of supply routes made delivery difficult.

“They are getting help,” the opposition figure said, “but the other side is much stronger and better equipped and trained.”

Det bemerkelsesverdige er fremgangen og at Hizbollah er med. Krigen er ved å anta en mer sekterisk karakter, og det gjør at alle parter mobiliserer maksimalt, også Hizollah i Libanon. De vet hvilken skjebne som venter shiaene i Syria hvis al-Nusra-fronten vinner.

The battle has brought Hezbollah’s role in Syria to the forefront as the war becomes a regional conflict, pitting Shiite-led Iran, the main backer of Mr. Assad and Hezbollah, against the Sunni Muslim states and their Western allies that support the uprising.

Tensions have risen in Lebanon as Syrian rebels have shelled Hezbollah-controlled areas. On Sunday, they hit the Lebanese town of Hermel with Grad missiles, activists said.

Ali, a Shiite from southern Lebanon, said Sunday that one of his relatives was fighting with Hezbollah in Qusayr and reported in a text message: “Things are fine. They are perfect.”

He said he supported Hezbollah’s intervention in Syria because it would deter the rise of Sunni extremist groups like Al Nusra Front among the rebels.

“If we don’t defend our villages,” he said, referring to Shiite villages in Syria, “Al Nusra will be outside our homes the next day.”

Lebanese news media and residents of the Bekaa Valley bordering Syria have reported a recent increase in the funerals of Hezbollah fighters who have been fighting near Qusayr. One resident described Lebanese Shiites in the area as being concerned about relatives recently deployed to Syria by Hezbollah.

“They are soldiers — they have to go,” the resident said.